Anhydrous lenalidomide form-i

ABSTRACT

Anhydrous polymorphic form-I of anti cancer drug, Lenalidomide whose chemical name is 3-(4-amino-1-oxo-1,3-dihydro-isoindole-2-yl)-piperidine-2,6-dione, is disclosed. Alternate methods for making anhydrous polymorphic form-I of Lenalidomide are also disclosed.

The present invention relates to anhydrous polymorphic form-I ofLenalidomide, whose chemical name is3-(4-amino-1-oxo-1,3-dihydro-isoindole-2-yl)-piperidine-2,6-dione.Lenalidomide is an anti cancer drug useful in the treatment ofmyelodysplastic syndrome. The invention also relates to alternateprocesses for the preparation of anhydrous polymorphic form-I ofLenalidomide.

PRIOR ART

Various polymorphic forms of3-(4-amino-1-oxo-1,3-dihydro-isoindole-2-yl)-piperidine-2,6-dione (alsocalled by its generic name—Lenalidomide) are reported in patentapplication US 2005/0096351 A1. In this patent invention, variouspolymorphic forms such as Form-A, Form-B, Form-C, Form-D, Form-E,Form-F, Form-G and Form-H have been reported. The representative figureof powder X-ray diaffractograms, DSC, TGA thermographs and UV-visiblespectra of all these polymorphic Form-A to Form-H are mentioned in thispatent application. It is also reported in this patent application thatthe polymorphic Form-A is anhydrous form and no moisture content given.Polymorphic form-B is hemi hydrate with moisture content of 3.1%.Polymorphic Form-C is a hemi-solvate of acetone and form-D is solvatedwith water and acetonitrile. Form-E is a dihydrate with a moisturecontent of 11.9%. Form-F is an unsolvated material and is obtained bycomplete dehydration of Form-E material. Form-G is also an unsolvatedand is obtained by slurrying Form-B and Form-E in tetrahydrofuransolvent. The water contents for Form-F and G are not given in thedescription and examples. Form-H is a crystalline solid hydrated withabove 0.25 moles of water.

Form-A:

The processes for making these polymorphic forms are also given in thepatent description very briefly. The temperature condition for thepreparation of anhydrous Form-A is given in a table-I of theabove-mentioned patent, heating Lenalidomide at 175° C. for 1 hour.Interconversion studies show that Form-B typically converts to Form-A ina tetrahydrofuran solvent system. De-solvation experiments show thatupon heating at 175° C. for about 5 min, Form-B typically converts toForm-A. It is also mentioned that Form A was obtained by crystallizationfrom various non-aqueous solvents including 1-butanol, butyl acetate,ethanol, ethyl acetate, methanol, methyl ethyl ketone, andtetrahydrofuran. Form A is a crystalline, unsolvated solid that melts atapproximately 270.degree. C. Also given in the patent text that Form Ais not hygroscopic and appears to be the most thermodynamically stableanhydrous polymorph of3-(4-amino-1-oxo-1,3-dihydro-isoindol-2-yl)-piperidine-2,6-Dione.

Form-B:

Form B, the hemihydrate, was also obtained by crystallization from thesolvents hexane, toluene and water. It is mentioned in the patentdescription that Lenalidomide Form-B is the desired polymorphic form foractive pharmaceutical ingredient (API) and this form has been used inthe formulation of API into drug product for clinical studies.

Amorphous polymorphic form of3-(4-amino-1-oxo-1,3-dihydro-isoindole-2-yl)-piperidine-2,6-dione andLenalidomide methane sulfonic acid salt are reported and claimed inpatent application WO 2009/114601 A2. The representative figure ofpowder X-ray diaffractograms, DSC and TGA thermographs of amorphouspolymorphic Form is mentioned in this patent application. In theexamples 3 and 4 process for making Lenalidomide and their powder X-raydiaffractograms are given (FIGS. 7 and 8) but not claimed.

Acid addition salts and their polymorphic forms of3-(4-amino-1-oxo-1,3-dihydro-isoindole-2-yl)-piperidine-2,6-dione arereported and claimed in patent application WO 2009/111948 A1. Therepresentative figures of powder X-ray diaffractograms and IR spectraare given.

PRESENT INVENTION

In search of finding for new polymorphs of Lenalidomide, we surprisinglyfound an stable anhydrous form, which is obtained by distillingpartially or completely the solvents dimethylformamide, isopropylalcohol or acetonitrile solvents containing Lenalidomide or its hydratedforms under normal atmospheric pressure or at reduced pressures and alsoby azeotropic distillation in toluene and other suitable solvents. Thethus obtained anhydrous novel form is very stable at room temperature(25-35° C.) and is not absorbing water or converting to any reportedhydrated forms. After storage for more than a year at room temperature(25-35° C.) the anhydrous form is not converted into any hydrated fromsuch as Form-B (hemihydrate) or Form-E. The moisture content in theazeotropically distilled material is always less than 0.1%.

The anhydrous polymorphic form of Lenalidomide, hereinafter called asForm-I, is obtained, after the completion of the catalytic reduction ofnitro group of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione and then filteration of thecatalyst followed by removal of solvent dimethyl formamide, undervacuum. The Form-I can also be obtained by suspending the wetLenalidomide cake, which is obtained directly after filtration of thecatalyst from the reaction mass, in solvents such as isopropyl alcohol,dimethyl formamide and acetonitrile followed by reducing or completelydistilling the solvents at temperatures varying 65° C. to 110° C. undervacuum or without vacuum and then finally drying at temperature varyingfrom 40-110° C. either under vacuum or without vacuum. Also theanhydrous polymorphic form-I of Lenalidomide is obtained by filterationand drying at temperature varying from 40-110° C. either under vacuum orwith out vacuum after azeotropically distilling the solvent toluenecompletely or partially with or without vacuum, at temperatures varying65° C. to 110° C.

The polymorphic Form-I prepared by above mentioned methods are havingidentical p-XRD, IR, TGA and DSC pattern.

Yet another invention of this patent application is the preparation ofthe hemihydrate form of Lenalidomide (Form-B as per US 2005/0096351 A1)by an alternate method. In the patent US 2005/0096351 A1, the preferredprocess parameters have been identified and given as 1.

1. Hot slurry temperature of 70-75° C.

2. Product filtration of 3-(4-amino-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6dione at 65-75° C.

3. Drying under vacuum at 60-70° C. is preferred for an efficientremoval of unbound water in 3-(4-amino-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6dione wet cake.

4. The filtration step of3-(4-amino-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6dione may be atime sensitive operation. The use of efficient solid-liquid separationequipment is preferred.

5. Holding periods of water-wet cake of3-(4-amino-1-oxo-1,3-dihydro-isoindol-2-yl)-piperidine-2,6dione at KFhigher than 5% may cause the kinetic equilibrations of polymorph B tomixed polymorphs of E and B.

Optimum conditions were determined to be 10 volumes of solvent (H₂O),70-80° C. for 6-24 hours.

Whereas in the present process, the crude Lenalidomide solid obtainedafter transfer hydrogenation or catalytic hydrogenation of3-(4-nitro-1-oxo-1,3 dihydro-isoindol-2-yl)-piperidine-2,6-dione iscompletely freed from the solvents such as dimethylformamide to obtainpolymorphic form-I or alternatively after distillation of the solventfrom the reaction mixture then the residue is reacted with molarequivalent of dilute hydrochloric acid and dissolved in water. Activatedcarbon is added to the solution and filtered through hyflo bed. Theclear filtered solution is neutralised and adjusted the pH to 7.5 to 8.0with a suitable base such as ammonia solution or aqueous solutions ofhydroxides, carbonates or bicarbonates of sodium, potassium or ammoniumto get the Lenalidomide precipitated. The filtered product is washedplenty of water to remove the inorganics, followed by drying undervacuum at temp 65° C. to 110° C. This is a very simple, reproducible andcommercially feasible process for making Lenalidomide Form-B. The IR,PXRD, TGA DSC of the thus obtained product are identical with theproduct obtained by following the optimized process given in the patent

BRIEF DESCRIPTION OF THE DRAWINGS

Specific aspects of the invention can be understood with reference tothe attached figures:

FIGS. 1 a and 1 b provide a representative powder X-ray diffraction(PXRD) pattern of Lenalidomide anhydrous Form-I, prepared by example-5;

FIG. 2 provides a representative IR spectrum of Lenalidomide anhydrousForm-I;

FIG. 3 provides a representative thermo gravimetric analysis (TGA) ofLenalidomide anhydrous Form-I;

FIG. 4 provides a representative differential scanning calorimeter (DSC)thermogram of Lenalidomide anhydrous Form-I;

FIGS. 5 a and 5 b provide a representative X-ray powder diffraction(XRPD) pattern of Form-B, which is prepared by example-4;

FIG. 6 provides a representative IR spectrum of Form-B, which isprepared by example-4;

The synthetic process for Lenalidomide starts from side chainbromination of 2-methyl-3-nitro-benzoate with N-bromosuccinimide in asuitable solvents such as chloroform, ethylene dichloride, carbontetrachloride, chlorobenzene, 1,2-dichlorobenzene or mixture of thesesolvents at temperature in the range of 60° C. to 135° C. to obtain2-bromomethyl-3-nitro-benzoate.

The 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dionesolid is obtained by alkylation followed by cyclisation of methyl2-bromomethyl-3-nitro-benzoate with d, 1-3-Aminoglutarimide in solventssuch as dimethylformamide, methanol, ethanol, acetonitrile and mixtureof these solvents. The thus obtained 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione has HPLC purity of above99.0% and is taken for the next stage without further purification.

By catalytic hydrogenation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione in solvents such asdimethylformamide, methanol, ethanol, isopropyl alcohol or mixture ofthese solvents at temperature 50-100.0° C. under pressure or bubbling ofhydrogen gas at atmospheric pressure, then filteration of the catalystfollowed by distillation under high vacuum Lenalidomide polymorphicform-I is obtained. The polymorphic form-I of Lenalidomide can also beobtained by transfer hydrogenation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione using solventsdimethylformamide, methanol, ethanol, isopropyl alcohol or mixture ofthese solvents at temperature 50-100.0° C. using ammonium formate orformic acid as source of hydrogen. The precious metal catalysts used inthe hydrogenation are Raney Nickel, palladium etc., followed byfilteration of catalyst and distillation of the solvent under highvacuum.

The purity of anhydrous polymorphic Form-I of Lenalidomide obtained bypurification from acid base treatment followed by distillation in thesolvents such as isopropyl alcohol or acetonitrile solvents is more than99.90% with any single impurity level by not exceeding 0.10%. Themoisture content is always less than 0.1%. The anhydrous polymorphicForm-I of Lenalidomide is characterized by 1H NMR, 13C NMR and Massspectra.

The Powder XRD 2θ° values of the anhydrous Form-A of Lenalidomidereported in the patent application US 2005/0096351 A1 are compared withthe Powder XRD 2θ° values of polymorphic Form-I reported in the presentinvention and differences are tabulated in the following table-I

TABLE I Comparision of 2θ° values between Form-A and Form-I of thepresent invention 2θ° Values of Form-I of 2θ° Values of patent (Form-A)S. NO. present invention Sample 01  7.793 About 8 (Single peak) (Twosignificant peaks) 02 10.120 03 11.201 04 14.285 05 14.766 14.5 0615.716 07 16.173 16.0 08 17.586 17.5 09 18.375 10 20.030 11 20.493 20.512 22.648 13 23.660 14 24.029 24.0 15 24.747 16 25.187 17 25.910 26.0 1828.261 19 32.521 20 33.485 21 34.858 22 43.170

DETAILED DESCRIPTION FOR THE PREPARATION OF LENALIDOMIDE FORM-I

The anhydrous polymorphic Form-I of Lenalidomide can also be prepared bytaking the hydrated Form-B or Form-E of Lenalidomide in a solvent suchas isopropyl alcohol or in acetonitrile and the temperature is increasedto refluxing. After maintaining for about one hour the solvent ispartially distilled under atmospheric pressure. Moisture content ischecked for the distilled solvent and if expected amount of water in thereaction mass is completely removed the reaction mass is cooled and theproduct is filtered. If necessary further solvent can be removed bypartial distillation to expel the water in the product. Alternativelythe solvent is completely distilled off from the vessel either byatmospheric distillation or under vacuum and upon cooling a co-solventsuch as hexane, heptane, cyclohexane, toluene or ethyl acetate is addedto the residue and the product is slurried and filtered.

The polymorphic Form-I of Lenalidomide can also be prepared by takingthe hydrated form of Lenalidomide in a solvent such as toluene, xyleneor cyclohexane and the water in the product is completely separated byazeotropic distillation. After water removal by azeotropic distillation,the reaction mass is cooled and the product is filtered. Alternativelythe solvent is completely distilled off from the vessel either byatmospheric distillation or under vacuum and upon cooling a co solventsuch as hexane, heptane, isopropyl alcohol or ethyl acetate are added tothe residue and the product is slurried and filtered.

The filtered wet product is dried at a temperature varying from 40-110°C. either under vacuum or with out vacuum till the residual solvents areunder specified limits.

FIG. 1 shows a representative P-XRD pattern of Form-I. The pattern ischaracterized by peaks, preferably significant peaks, at (2θ) 7.793(distinct single peak), 10.120, 11.201, 14.285, 14.766, 15.716, 16.173,17.586, 18.375, 20.030, 20.493, 22.648, 23.660, 24.029, 24.747, 25.187,25.910, 28.261, 32.521, 33.485, 34.858, 43.170.

Representative IR spectra, DSC thermograph and TGA thermographs areprovided in FIGS. 2, 3 and 4 respectively.

Representative thermal characteristics of Form polymorphic Form-I areshown in FIG. 2.

The DSC curve of Form A exhibits an endotherm at about 270.° C.

TGA data show no weight loss up to about 150° C., indicating anunsolvated or anhydrous material. Weight loss above 150° C. isattributed to decomposition.

The moisture content of the Form-I samples prepared is always less than0.1% Form B

The hemihydrate form of Lenalidomide (reported as polymorphic Form-B asper patent application US 2005/0096351 A1) is also prepared by analternate method. The crude Lenalidomide solid obtained afterhydrogenation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione is reacted with dilutehydrochloric acid and dissolved in water. Activated carbon is added andfiltered through hyflo bed. The clear filtered solution is neutralisedand adjusted the pH to 7.5 to 8.0 with a suitable base such as ammoniasolution or solutions of hydroxides, carbonates or bicarbonates ofsodium, potassium or ammonium to get the Lenalidomide precipitated.Filtered and washed the precipitate with plenty of water to remove theinorganics. Dried the wet product in a vacuum oven to obtain hemihydrateform of Lenalidomide with a HPLC purity of above 99.9%.

The hydrogenation step can be carried out by using Palladium or RaneyNickel as catalyst and can be carried out under hydrogen pressure in ahydrogenarator or by bubbling hydrogen gas in a conventional reactor atatmospheric pressure. And also the reduction of nitro group step can bealso be carried out by transfer using Palladium as catalyst and formicacid or ammonium formate as source of hydrogen in a conventional reactorat atmospheric pressure. By using a conventional reactor in the transferhydrogenation or in the catalytic hydrogenation with hydrogen gasbubbling at atmospheric pressure usage of speciality and expensiveequipment such as pressure hydrogentator vessel can be avoided. Afterthe hydrogenation is complete the catalyst is filtered and the clearfiltered solution is neutralised and adjusted the pH to 7.5 to 8.0 witha suitable base such as ammonia solution or solutions of hydroxides,carbonates or bicarbonates of sodium, potassium or ammonium to getLenalidomide precipitated. Filtered and washed the precipitate withplenty of water to remove the inorganics. Dried the wet product in avacuum oven to obtain hemihydrate form of Lenalidomide with a HPLCpurity of above 99.9%. The purification of Lenalidomide by acid basetreatment is a very simple and inexpensive. This process is not reportedin the literature and is a novel purification step in the synthesis ofLenalidomide. This process is feasible on a commercial scale.

The synthetic process for Lenalidomide starts form side chainbromination of 2-methyl-3-nitro-benzoate with N-bromosuccinimide insuitable solvents such as chloroform, ethylene dichloride, carbontetrachloride, chlorobenzene, 1,2-dichlorobenzene or mixture of thesesolvents at temperature in the range of 60° C. to 135° C. to obtain2-bromomethyl-3-nitro-benzoate. The product obtained is2-bromomethyl-3-nitro-benzoate having a HPLC purity of over 99.0%.

The 3-(4-nitro-1-oxo-1,3 dihydro-isoindol-2-yl)-piperidine-2,6-dionesolid is obtained by alkylation followed by cyclisation of methyl2-bromomethyl-3-nitro-benzoate with (d, 1)-3-aminoglutarimide insolvents such as dimethylformamide, methanol, ethanol, acetonitrile andmixture of these solvents. The thus obtained 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione is having HPLC purity ofabove 99.0% and is taken for the next stage with out furtherpurification.

The crude Lenalidomide is obtained by catalytical hydrogenation of3-(4-nitro-1-oxo-1,3 dihydro-isoindol-2-yl)-piperidine-2,6-dione insolvents such as dimethylformamide, methanol, ethanol, isopropyl alcoholor mixture of these solvents at temperature 50-100.0° C. under pressureor bubbling of hydrogen gas at atmospheric pressure. The crudeLenalidomide can also be obtained by transfer hydrogenation of3-(4-nitro-1-oxo-1,3 dihydro-isoindol-2-yl)-piperidine-2,6-dione usingsolvents dimethylformamide, methanol, ethanol, isopropyl alcohol ormixture of these solvents at temperature 50-100.0° C. using ammoniumformate or formic acid as source of hydrogen. The precious catalystsused in the hydrogenation are Raney Nickel, palladium etc.,

The purity of anhydrous polymorphic form of Lenalidomide obtained bypurification from acid base treatment followed by distillation in thesolvents such as isopropyl alcohol or acetonitrile solvents is more than99.90% with any single impurity by not more than 0.10%. The moisturecontent is always less than 0.1%. The anhydrous polymorphic form ofLenalidomide is characterized by 1H NMR, 13C NMR and Mass spectra.

We have compared the Powder XRD 2θ° values of the form-B samples ofLenalidomide prepared with that of the Powder XRD 2θ° values for theForm-B in the patent application US 2005/0096351 A1 and found that theboth the values are exactly matching. The IR spectrum is also concordantwith that of the reported. The TGA thermograph and the DSC spectrum arealso comparable with that of sample prepared by this applicationprocedure.

Thermal Stability of Lenalidomide Form I

The lenalidomide Form I obtained after drying temperature 65 to 75° C.under vacuum is taken subjected to heating at 95 to 105° C. in oil bath,kept in rotator vapor for 7 days, cool to room temperature and thesample is analyzed per IR, NMR, XRPD (X-ray powder diffractometry), DSC(differential scanning calorimetry) & TGA (thermogravimetry). No changeis observed in spectral data. The moisture content is also determinedfor sample and found to be less than 1%. No further change in impurityprofile is observed.

Representative thermal characteristics of Form A are shown in FIG.

TGA data show a small weight loss up to about 150° C., indicating anunsolvated material. Weight loss above 150° C. is attributed todecomposition On the basis of our work weight loss between 25° C. and225° C. is 0.13%.

The DSC curve of Form A exhibits an endotherm at about 266.64° C.

Accelerated Stability Studies

The lenalidomide Form I sample are subjected to accelerated stabilitystudies under following conditions & analyzed at initial after 1, 2, 3and 6 months.

Condition 1—temperature: 40° C.±2° C.

-   -   Relative humidity: 75% RH±5%

Condition 1—temperature: 30° C.±2° C.

-   -   Relative humidity: 65% RH±5%

We have not observed major deviation in quality of samples analysed ofinitial samples after 1,2, 3 and 6 months.

The moisture content is marginally increased from 0.09% w/w to 0.21%w/w. No increase in impurity profile is observed in 1,2, 3 and 6 monthssample. So under the above stress condition the lenadomide Form I sampleis not converted in any of the hydrated polymorphic form such hemihydrated & dihydrate Form E.

Intrinsic Dissolution and Solubility Studies Dissolution

Dissolution experiments were carried out in a ELECTROLAB-8 dissolutionapparatus equipped with a ETC-112 temperature controller. An intrinsicdissolution apparatus (Woods apparatus) was used. Samples werecompressed at 2.0 metric tons for 1 min in KBr hydraulic press, giving asample surface of 0.50 cm². A dissolution medium consisting of 900 mLHCl buffer, pH 1.8, with 1% sodium lauryl sulfate, was used for eachexperiment. The medium was degassed by vacuum filtration through a0.45-μm nylon filter disk and maintained at 37° C. The apparatus wasrotated at 50 rpm for each experiment. Aliquots were filteredimmediately using 0.45-μm nylon syringe filters. In some cases, theundissolved solids were recovered and analyzed by X-ray powderdiffraction (XRPD).

Solubility

Equilibrium solubility experiments were conducted in a 100-mL,three-neck, round-bottom flask immersed in a constant temperature oilbath maintained at 25° C. A solid sample of 450 mg was stirred in 50 mLof dissolution medium (HCl buffer, pH 1.8, with 1% sodium laurylsulfate) using a mechanical stir rod. Aliquots were filtered andcentrifuged at 3500 rpm using 0.2-μm nylon syringe filters andimmediately diluted 1 mL→50 mL, then 5 mL→425 mL with dissolutionmedium. In some cases, the undissolved solids were recovered and sentfor X-ray powder diffraction (XPRD) studies.

Results:

Both the solubility and dissolution experiments were conducted in amedium of HCl buffer, pH 1.8, containing 1% sodium lauryl sulfate. Thesolubilities were estimated to be 3.15 mg/ml for Form 1 & 3.28 mg/ml forForm B, respectively. The dissolution rates of Forms-I & Form-B wereestimated to be 421 mg/min/cm² & 0.250 mg/min/cm² respectively.

Whereas the solubilities of both the Form-I and Form-B are similar,there is a high dissolution rate can be seen in Form-I compared toForm-B

Humidity Test

The anhydrous form of lenalidomide along with two batches (0812/006 &0812/007 &) were subjected for humidity test.

Experimental

NaBr, NH4Cl, KOH, Na2HPO4 were used as Saturated solution at temperature25.1° C., 25° C., 24.7° C., 26.8° C. and humidity 84%, 79%, 23%, 93%respectively at initial water content of 0.08%.

Result

The water content after humidity test were 0.21% w/w, 0.13% w/w, 0.12%w/w, 0.10% w/w respectively.

Hence it is seen that humidity has no impact on the moisture content ofthe Form-I.

Formulation

The sample of lenalidomide Form I API is encapsulated & compared withthe REVLIMID capsules. The XRPD (X-ray powder diffractometry) of theencapsulated material of Lenadomide Form I is showing distinct peak at7.786 2θ° value.

A distinct peak at 2θ° value of 7.786 that is characteristics peak oflenadomide Form I.

The polymorphic form of lenalidomide Form I is not changed even afterencapsulation. The XRPD spectra of encapsulated material withoutlenadomide Form I API is also taken & major 2θ° values are deleted withXRD spectra of the Lenadomide capsules & compared the major peaks withREVILIMID capsules & found that peak are not matching.

The moisture content of the lenalidomide encapsulated material made withForm I is having 0.08% where as REVILIMID capsules is having 2.35%

The moisture content also shows that the polymorphic Form I is notchanged to any of the hydrated form, and hence stable.

Bulk Density

We observed the following bulk density for three batches

I. Batch No—0812/005

Untapped Density—0.278 g/ml

Tapped density—0.465 g/ml

II. Batch No—0812/006

Untapped Density—0.286 g/ml

Tapped density—0.481 g/ml

III. Batch No—0812/006

Untapped Density—0.286 g/ml

Tapped density—0.481 g/ml

The following are the examples for the preparation of novel polymorphicForm-I and polymorphic Form-B are not limited to the scope of invention.

Examples

1. Preparation of methyl 2-bromomethyl-3-nitro-benzoate:

Into a 2.0 L 4-necked RB flask charged 100.0 g of methyl2-methyl-3-nitro benzoate, 8.3 g of AIBN, 272.0 g of N-bromo succinimideand 1.5 L chlorobenzene under nitrogen atmosphere. Raised thetemperature of the reaction mass to 90-95° C. Maintained the mass undermaintenance temp. of 90-95° C. for about 6 hrs. The progress of thereaction is monitored by TLC. After TLC complies cool the mass totemperature 25 to 30° C. Filtered the mass and wash with methylenechloride. Washed the organic layer with DM water in two portions. Washedthe organic layer with saturated aqueous sodium bicarbonate solution.Washed the organic layer with saturated sodium chloride solution. Driedthe organic layer over sodium sulphate and filter. Distilled off thesolvent completely under vacuum. Weight of crude oil is 120.0 g. To theabove crude oil charged 600.0 ml of n-hexane. Stirred at temp. of 25-30°C. for 1 hr. Cooled the reaction mass temperature to 0-5° C. andmaintain for 20-30 minutes Filtered the material and wash with 100 mL ofHexane. Weight of the wet material is 110.0 g. Dried the wet compound at40-50° C. till constant weight is obtained.

Dry weight of the compound—100.0 g

1H NMR Spectra: δ values—4.00 (s, OCH3), 5.15 (s, CH ₂), 7.52-7.56 (t,Ar-H), 7.95-7.97 (d, Ar-H), 8.10-8.11 (d, Ar-H).

13C NMR Spectra: δ values—22.69 (CH₂Br), 53.02 (OCH₃), 127.77 (Ar-C),129.08 (Ar-C), 132.3 (Ar-C), 1327.57 (Ar-C), 134.66 (Ar-C), 150.50(Ar-C), 165.80 (C═O),

2. Preparation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione:

Into a 2.0 L dried 4 necked round bottom flask equipped with acondenser, an addition funnel and nitrogen gas bubbler under stirring,charged 50.0 g of methyl 2-bromomethyl-3-nitro-benzoate, 29.2 g ofracemic 3-amino-piperidine-2,6-dione and 835.0 ml of DMF. Chargedtriethyl amine to the reaction mass at 25-35° C. in about 30-45 min.Raise the mass temperature to 95-100° C. Maintained the reaction mass at95-100° C. for 6-6½ hrs under nitrogen atmosphere. The progress of thereaction is monitored by TLC. Poured the reaction mass slowly into 2.6 Lof DM water at 25-35° C. under stirring in about 30-45 min. Maintainedthe reaction mass at 25-35° C. for 60-90 min under stirring. Filteredthe material under vacuum, wash the wet cake with 215.0 ml of DM water,suck died the material. Dried the wet material in a oven at 60-65° C.for 4-5 hours. Weight of the dry material is—30.0 g.

3. Preparation of Lenalidomide Technical Grade Material

Into a 5.0 L 4 necked RB flask, charged 100.0 g of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione, 10.0 g of 10% Pd/C and 3200ml of DMF under nitrogen atmosphere. Stirred the mass and raise thereaction mass temperature to 60 -65° C. Started the hydrogen gasbubbling into reaction mass at temperature 60-65° C. for 6 hours. Theprogress of the reaction is monitored by TLC. Cooled the mass totemperature 25to 30° C. Filtered the catalyst Pd/C under plant vacuum inthe presence of nitrogen atmosphere and wash with dimethylformamide; wetPd/C is transferred into a polythene bag for recovery. Distilled off theabove organic layer solvent completely under vacuum below 60° C. Chargedethyl acetate 800 ml (lot-I) to the mass and stirred for 60 min.Filtered the solid and wash with 200 mL of ethyl acetate (Lot-II). Driedthe above wet material in a oven at temperature 65-75° C. for 120-180min. Dried Weight of the compound is 78.0 g.

4. Purification of Lenalidomide to get Form-B material.

Into a 1.0 L 4-necked round bottom flask, charged 20 g of Lenalidomidecrude, and DM water 600 ml (Lot-I). Maintained stirring at temperature25-35° C. for 5-10 min. Added Conc.HCl to the mass at 25-35° C. (pH ofthe mass is to be adjusted to 1-1.5) Maintained the mass at temperature25-35° C. for 10-15 min. After clear solution formation is observed,charged carbon to the mass. Maintained the mass at temperature 25-35° C.for 10-15 min. Filtered the mass on hyflow bed under plant vacuum andwash with DM water. Transfered the above filtrate into a 1.0 L 4-neckedround bottom flask, added ammonia solution to the filtrate and adjustthe pH of the mass to 8-9. Maintained the mass at temperature 25-35° C.for 60-90 min. Filtered the mass under plant vacuum and washed with 10ml of DM water, suck dried.

Dry Weight: 18.0 g.

Dried the wet material in a drier at temp 60-70° C. for 1.5 to 2.0 hrsunder vacuum. The sample is analysed for moisture content, IR spectra,DSC, and Powder XRD.

The results are exactly matching with that of the values reported in thepatent application US 2005/0096351 for polymorphic Form-B.

5. Purification of Lenalidomide to get Form-I material.

Into 500 mL 4-neck round bottom flask, charge the above dry material (ofthe example 4) and IPA (200.0 ml). Raised the reaction mass temperatureto 80° C. Maintained the mass at temperature 80-85° C. for 90-120 min.Started the distillation of IPA using downward distillation apparatus[Till MC decrease in the mass and sample IR matches with STD anhydroussample]. Cooled the mass to temperature 25 to 30° C. Maintained the massat temperature 25-35° C. for 60-90 min. Filtered the mass under plantvacuum, washed the wet cake with 10 ml of IPA and suck dried for 10 min.Dried the material at temperature 65-75° C. for 2-3 hrs. Dried Weight ofthe compound is—14.5 g. Dried sample is analysed for moisture content,IR spectra, TGA, DSC, and Powder XRD.

Powder XRD: 2θ° Value 7.793, a distinct single peak. Also significantpeaks are observed at 2θ Values 10.175, 11.269, 14.327, 15.772, 16.277,17.646, 20.099, 20.508, 23.728, 24.098, 25.230, 25.987, 28.320, 32.595,

DSC Thermograph: Peak maxima—266.64° C.

TGA Thermograph: Weight loss between 25° C. and 225° C. is 0.13%

IR Spectra: 3409.0, 3345.0, 3092.2, 1706.5, 1674.0, 1605.7, 1341.3,1242.6, 1209.5, 882.0, 745.1 cm⁻¹

1. A process for producing an anhydrous polymorphic form of lenalidomide(Form 1), which comprises either: (i) distilling a solution oflenalidomide in dimethylformamide, isopropyl alcohol, or acetonitrile;or (ii) distilling azeotropically a solution of lenalidomide in toluene,xylene or chlorobenzene; to obtain lenalidomide of Form I.
 2. A processaccording to claim 1 which comprises: a) side chain bromination of2-methyl-3-nitro-benzoate with N-bromosuccinimide in suitable solventssuch as chloroform, ethylene dichloride, carbon tetrachloride,chlorobenzene, 1,2-dichlorobenzene or mixture of these solvents attemperature in the range of 60° C. to 135° C. to obtain2-bromomethyl-3-nitro-benzoate; b) obtaining 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione solid by alkylation followedby cyclisation of 2-bromomethyl-3-nitro-benzoate with d,1-3-aminoglutarimide in solvents such as dimethylformamide, methanol,ethanol, acetonitrile and mixture of these solvents; c) obtaininglenalidomide by: (i) catalytical hydrogenation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione, using Raney Nickel orpalladium, in solvents such as dimethylformamide, methanol, ethanol,isopropyl alcohol or mixture of these solvents at temperature 50-100.0°C. under pressure or bubbling of hydrogen gas at atmospheric pressure;or (ii) transfer hydrogenation of 3-(4-nitro-1-oxo-1,3dihydro-isoindol-2-yl)-piperidine-2,6-dione using solventsdimethylformamide, methanol, ethanol, isopropyl alcohol or mixture ofthese solvents at temperature 50-100.0° C. using ammonium formate orformic acid as source of hydrogen; d) reacting the crude lenalidomidewith dilute hydrochloric acid, and treating with activated carbon toneutralise the clear filtered solution, adjusting the pH to 7.5 to 8.0with a suitable base such as ammonia solution or solutions ofhydroxides, carbonates or bicarbonates of sodium, potassium or ammoniumto precipitate the lenalidomide, filtering and washing the precipitatewith water to remove inorganics; e) either (i) taking the wetlenalidomide in a solvent such as isopropyl alcohol or in acetonitrileand increasing the temperature is to reflux, maintaining at refluxtemperature, preferably for one hour, and partially distilling solventunder atmospheric pressure or under vacuum, cooling the mass to 30±5°C.; or (ii) removing water by azeotropic distillation from solvents suchas toluene, xylenes or chlorobenzene; f) filtration; and g) drying attemperature varying from 40-110° C. either under vacuum or withoutvacuum to obtain the lenalidomide of polymorphic Form-I.
 3. An anhydrouscrystalline polymerphic form of lenalidomide (Form 1) obtainable by theprocess of claim
 1. 4. The crystalline polymorphic Form-I oflenalidomide of claim 3 that has a moisture content of less than 0.5%.5. The crystalline polymorphic Form-I of lenalidomide of claim 4 thathas a moisture content of less than 0.2%.
 6. The crystalline polymorphicForm-I of lenalidomide of claim 3 that has a differential scanningcalorimetry melting temperature maximum of about 266° C.
 7. Acrystalline anhydrous polymorphic Form-I of lenalidomide, which ischaracterized by its Powder XRD 2θ value 7.793, a distinct single peak.8. The crystalline polymorphic Form-I of lenalidomide of claim 7,wherein the powder XRPD pattern further comprises significant peaks at10.175, 11.269, 14.327, 15.772, 16.277, 17.646, 20.099, 20.508, 23.728,24.098, 25.230, 25.987, 28.320, 32.595.
 9. The crystalline anhydrouspolymorphic Form-I of lenalidomide according to claim 7 which has amoisture content as defined in claim 4, and/or a differential scanningcalorimetry melting temperature maximum as defined in claim
 6. 10. Apharmaceutical composition comprising crystalline polymorphic Form-I of3-(4-amino-1-oxo-1,3 dihydro-isoindol-2-yl)-piperidine-2,6-dione asclaimed in claim 3 and a pharmaceutically acceptable excipient.
 11. Amethod of treating or ameliorating cancer comprising administering atherapeutically effective amount of an anhydrous crystalline polymorphicform of lenalidomide (Form-I) as defined in claim 3 or 7 to a subject inneed thereof.
 12. A method according to claim 11 wherein the cancer ismyelodysplastic syndrome.